Starting circuit for induction motor

ABSTRACT

A circuit for the automatic starting of an induction motor of the type having a main or running winding and at least one phase or starting winding. The starting circuit comprises a current sensing means which is series connected with the main or running winding to a source of electrical power. Said sensing means is also series connected to the combination of a memory circuit and a threshold detection means. The high current drawn by the main or running winding, when initially energized, is sensed by the current sensing means and, when sufficiently high, a signal is passed to an interfacing device between a power source and the starting winding by the memory circuit and the detection means calibrated to pass the signal at voltages in excess of that voltage of the signal which exists when the motor is running at normal speed. This signal is present at the gate of the interfacing device during the entire time that the phase or starting winding is to be energized. The interfacing device, in turn, connects the phase or starting winding of the motor to the power source. When the motor approaches normal running speed and the initial high current drawn by the main or running winding diminishes, the phase or starting winding of the motor will be disconnected from the power source through the action of the calibrated detection means, the memory circuit and deenergization of the gate of the interfacing device.

United States Patent [191 Scheuer et al.

[4 1 Oct. 9, 1973 STARTING CIRCUIT FOR INDUCTION MOTOR [73] Assignee:Design & Manufacturing Corporation, Connersville. Ind.

[22] Filed: May 27, 1971 [21] Appl. No.: 147,506

Related US. Application Data [63] Continuation-in-part of Ser. No.22,552, March 25,

1970, abandoned.

Primary Examiner-Gene Z. Rubinson Attorney-Melville, Strasser, Foster &Hoffman [57] ABSTRACT A circuit for the automatic starting of aninduction motor of the type having a main or running winding and atleast one phase or starting winding. The starting circuit comprises acurrent sensing means which is series connected with the main or runningwinding to a source of electrical power. Said sensing means is alsoseries connected to the combination of a memory circuit and a thresholddetection means. The high current drawn by the main or running winding,when initially energized, is sensed by the current sensing means and,when sufficiently high, a signal is passed to w an interfacing devicebetween a power source and the starting winding by the memory circuitand the detection means calibrated to pass the signal at voltages inexcess of that voltage of the signal which exists when the motor isrunning at normal speed. This signal is present at the gate of theinterfacing device during the entire time that the phase or startingwinding is to be energized. The interfacing device, in turn, connectsthe phase or starting winding of the motor to the power source. When themotor approaches normal running speed and the initial high current drawnby the main or running winding diminishes, the phase or starting windingof the motor will be disconnected from the power source through theaction of the calibrated detection means, the memory circuit anddeenergization of the gate of the interfacing device.

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STARTING CIRCUIT FOR INDUCTION MOTOR CROSS-REFERENCE TO RELATEDAPPLICATION This is a continuation-in-part of the copending, nowabandoned application of the same inventors, Ser. No. 22,552, filed Mar.25, I970 and entitled STARTING CIRCUIT FOR INDUCTION MOTOR.

BACKGROUND OF THE INVENTION I. Field of the Invention The presentinvention relates to an automatic starting circuit for an inductionmotor, and more particularly for an induction motor of the type having amain or running winding and at least one phase or starting winding.

2. Description of the Prior Art In general, motors of the induction typecommonly used in high torque applications are built with a winding usedfor economical running operation (hereinafter called the main or runningwinding), and a second winding (hereinafter called the starting winding)used only momentarily to assist the main winding in rapidly attaining arunning speed in the desired direction. Such motors are normallyequipped with internal centrifugal switches that automatically energizethe starting winding, whenever the rotor speed is below a predeterminedlevel.

Where external switching is required, for servicing purposes or otherreasons, a current operated relay, closely calibrated for theapplication, is used and is located externally of the motor. The coil ofsuch relay, being series connected with the main winding of the motor,magnetically moves an armature at a predetermined level of electricalcurrent. It will be understood by one skilled in the art that thecurrent in the main winding is considerably higher at low rotor speeds.Contacts affixed to or operated by the relay armature are seriesconnected with the starting winding of the motor, causing it to beenergized until a desirable operating rotor speed is attained.

Neither the internal centrifugal switching devices nor the externallylocated electro-magnetic devices are capable of offering the high levelof reliability often required by the present day applications to whichsuch induction motors are put. This is true because of arcing and wearproblems associated with centrifugal switching devices and the relianceon very small forces for the operation of electromagnetic devices. Inaddition, it has been found that failure of the relay-type switch ismost often the result of insufficient force available to break apartcontacts that have been slightly welded by the motor currents beingswitched. Such failure may result in the destruction of the motor beingcontrolled.

Another approach is taught in United States Letters Pat. No. 3,226,620.This patent teaches the use of a magnetic coupling to monitor the mainwinding current and the use of the resulting signal to energize thestarting winding each half cycle of the line voltage, while the mainwinding current is above the normal running value. This method, however,requires the prediction of and correction for the phase relationship ofthe line voltage and the main winding current, so that the startingwinding will be energized near the zero crossing of the line voltage.This action is known to those skilled in the art as zero pointswitching. The correction for the phase shift is accomplished by fixedcomponents and the system is therefore sensitive to variations in thephase relationship.

In United States Letters Patent No. 3,414,789 a start signal is sent tothe gate of an interfacing device and the characteristics of theinterfacing device itself are depended upon to establish on and offthresholdsv However, thresholds established in this manner are notconsistent, due to variations in the characteristics of the interfacingdevice.

The circuitry of the present invention is characterized by a high levelof reliability. There are no moving parts; no dependence on triggeringaction initiated by marginal mechanical force; and no air-gap contactscontrolling large inductive currents. This circuitry is also notsensitive to variations in the phase relationship in the motor and zeropoint switching is accomplished always. In addition, the circuitry ofthe present invention is adaptable to perform the motor start functionfor a reversing motor, as will be shown hereinafter.

Finally, the circuitry of the present invention may be provided with abi-level threshold detection means to establish a first threshold forthe signal to turn on the starting winding and a second threshold forthe signal to turn off the starting winding, whereby to stabilize theaction of the interfacing device. This is particularly useful ininstances where the difference between the sensed voltage during themotor starting condition and the sensed voltage during the motor runningcondition is small.

SUMMARY OF THE INVENTION In its most basic form, the inventioncomtemplates the use of a sensing means, a memory circuit and athreshold detection means.

In one embodiment of the present invention the sensing means is a smallsensing transformer. The primary portion of the transformer is connectedin series with the running winding of an induction motor. The secondaryportion of the transformer supplies a voltage signal output that isessentially proportional to the current drawn by the motor runningwinding.

When power is applied to the running winding of the motor, the highcurrent initially drawn in trying to start the rotor passes through theprimary winding of the transformer, creating a relatively high level oftime varying magnetic flux which induces a relatively high voltage levelin the secondary winding. For purely sinusoidal current, this voltage issubstantially equal to the potential drop across the primary multipliedby the turns ratio of the transformer.

The transformer is specifically designed such that its output may beused to drive a memory circuit, which in turn drives a thresholddetection means in the form of a break-over device to energize the gateof an interfacing device or bi-directional semiconductor switchconnecting the starting winding of the motor to the source of electricalpower. The output of the transformer is converted to a DC signal whichis present during the entire time the starting winding is to beenergized. The last mentioned switch will conduct until the rotor of themotor has attained a suitable operating speed, as indicated by itsoperating current. At current levels near those occurring when the motoris running at normal speed, the voltage level of the transformer outputwill be insufficient to pass through the breakover device, causing thebi-directional semiconductor means, a memory circuit and thresholddetection means similar to that used in the first embodiment) is appliedto an induction motor having a running winding and two startingwindings, one for clockwise rotation of the rotor and one forcounter-clockwise rotation of the rotor.

The main winding of the motor is connected to a source of electricalcurrent through a bi-directional semiconductor switch, the gate of whichis energized by a signal from an integrated logic circuit.

The first and second starting windings of the motor are similarlyconnected to the source of electrical current by bi-directionalsemiconductor switches. The gate of each of these last mentionedswitches is connected to the output of the starting circuit through aswitching transistor. The bases of the switching transistors areconnected directly to signal outputs of the integrated logic circuit. Asignal from the logic circuit will be sent to one or the other of thetwo switching transistors at all times during the operation of themotor.

A third embodiment is similar to the second. However, the output of thestarting circuit is applied through a resistor to the base of atransistor which is connected between a DC source and the collectors oftwo switching transistors which are connected to the gates ofbi-directional semiconductor switches. The addition of the thirdtransistor and related components to the circuit of the secondembodiment serves to decrease the amount of current which the startingcircuit is required to supply to the two switching transistors by addinga stage of amplification.

A fourth embodiment illustrates the principles of the present inventionas applied to a device having a conventional timer means and a reversingmotor.

In the embodiment of the present invention, a resistor may besubstituted for the sensing transformer as a means of sensing the mainwinding current. Similarly, under some circumstances, a glow lamp orother bidirectional break-over device may be used in lieu of aunidirectional break-over device such as a zener diode.

Finally, the embodiment of the present invention may be provided with abi-level threshold detection circuit, such as a Schmitt trigger, as willbe described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I diagrammatically illustratesone embodiment of the starting circuit of the present invention.

FIG. 2 diagrammatically illustrates another embodiment of the startingcircuit of the present invention.

FIG. 3 diagrammatically illustrates another embodiment of the startingcircuit of the present invention similar to FIG. 2, but with means todecrease the amount of current required to be supplied to the switchingtransistors by the starting circuit.

FIG. 4 diagrammatically illustrates yet another embodiment of thestarting circuit of the present invention.

FIG. 5 diagrammatically illustrates an embodiment similar to FIG. 3wherein a resistor is substituted for the sensing transformer as a meansfor sensing the main winding current.

FIG. 6 diagrammatically illustrates the use of a glow lamp in lieu ofthe unidirectional zener diode.

FIG. 7 diagrammatically illustrates the circuit of FIG. 2 wherein asensing resistor is substituted for the sensing transformer.

FIGS. 8 and 9 are block diagrams of the primary elements of the startingcircuits of the present invention.

FIGS. 10 through 13 are simplified diagrammatic representations of theprimary elements of FIGS. 8 and 9, illustrating the use of a bi-levelthreshold detection circuit.

FIG. 14 illustrates the circuit of FIG. 2 provided with a bi-leveldetection circuit.

FIG. 15 illustrates the circuit of FIG. 3 provided with a bi-levelthreshold detection circuit.

FIG. 16 illustrates the circuit of FIG. 5 provided with a bi-levelthreshold detection circuit.

FIG. 17 illustrates the circuit of FIG. 16 wherein the output of thebilevel threshold detection circuit is transmitted to the interfacingdevices via a logic circuit.

FIG. 18 illustrates the circuit of FIG. 16 modified as shown in FIG. 13,with the memory circuit incorporated in the logic circuit.

FIG. 19 is similar to FIG. 18, but illustrates a portion of thethreshold detection circuit as incorporated. in a logic circuit.

FIG. 20 is similar to FIG. 18, but illustrates both the memory circuitand the bi-level threshold detection circuit as being incorporated inthe logic circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The starting circuits of thepresent invention may be used in substantially any application entailingthe operation of an induction motor having at least one startingwinding. For example, it may be used in association with an automatichousehold appliance. For purposes of an exemplary showing, theembodiments hereinafter described will be shown as used in an automaticdishwashing machine. It will be understood by one skilled in the artthat this application of the circuits of the present invention isexemplary only, and is not intended to be limiting.

FIG. 1 is a diagrammatic illustration of one embodiment of the startingcircuit of the present invention, as used in a typical dishwashingmachine. In general, automatic dishwashers are arranged to carry on aplurality of operations in sequence. The series of operations isfrequently referred to as cycles. For example, a typical automaticdishwasher is arranged to carry on in sequence a series of operationswhich may be designated as first wash, first rinse, second rinse, secondwash, third rinse, fourth rinse, dry.

The carrying on of this or some other cycle of operations is controlledby a timer which energizes or deenergizes substantially all of theelectro-mechanical machine components (such as solenoids, motors,lights, etc.). Various varieties of timers are well known in the art.Generally, a timer will comprise a motor. In some instances, the motordrives a device like a commutator which results in sequential and insome instances simultaneous opening and closing of electric switches. Inother instances, the timer motor drives a rotating element which isprovided with camming surfaces operating electric switches.

In the simplified diagrammatic illustration of FIG. 1, a timer 1 of anysuitable type is shown as being connected to a source of AC electricalcurrent 2 by means of lead 3. Lead 3 may contain a switch 4, which is adoor interlock switch, assuring that the machine is disconnected whenthe door is open. The timer 1 will contain and control a plurality ofswitches such as an endof-cycle switch 5, a water valve switch 6, aheater switch 7, a drain valve switch 8, and a motor power switch 9. Thewater valve, heater and drain valve are diagrammatically indicated at10, l1 and 12, respectively. The timer motor is shown at 13. A pilotlight may be provided as at 14. It will be understood by one skilled inthe art that the timer may control a plurality of additionalappurtenances (not shown) such as a timer rapid advance motor, adetergent dispenser and the like.

The induction motor of the'dishwasher is diagrammatically indicated bythe broken line rectangle 15. This motor may drive an impeller and/or apump means. The main or running winding of the motor is shown at 16 andthe starting winding is shown at 17. The motor may be provided with aprotective device such as a circuit breaker or the like. Such aprotective device is shown at 18.

The main or running winding 16 of the motor is connected through lead I9to the motor power switch 9 of the timer 1. The lead 19 contains theprimary portion a of a transformer 20. During a machine cycle, switches4 and 5 are closed and the running winding 16 will be connected to thepower source upon the closing of switch 9. Initially, a high currentwill be drawn by the running winding 16. For example, if the motor 15were a typical l/3 horsepower l 15 volt motor, the main winding woulddraw an initial current on the order of 18 amperes, which may induce apeak voltage level of about 18 volts in the secondary portion 20b of thesensing transformer 20.

Leads 21 and 22 extend from the secondary portion 20b of the sensingtransformer 20. Leads 21 and 22 are connected to the memory circuitcomprising a series combination of a rectifying diode 23 of any suitabletype and a capacitor 25.

The starting winding 17 of the motor 15 is connected to lead 19 by lead26. Lead 26 contains an interfacing device in the form of abi-directional semiconductor switch 27. The juncture of leads 21 and 24is connected by lead 28 to lead 26. The juncture of lead 22 and 24 isconnected to the gate of the bi-directional switch 27 through athreshold detection means comprising a break-over means 29. Thebreak-over means 29 may comprise a bilateral trigger diode, a glow lampor the like. For purposes of an exemplary showing it is illustrated asbeing a zener diode.

The AC voltage in the secondary portion 20b of the transformer 20 ispeak-detected (i.e., rectified as at 23 and filtered as at 25, thecombination of the diode and capacitor comprising a half-wave peakdetector) to form a DC signal which varies as the envelope of thevoltage in the secondary portion. Thus the diode 23 and capacitor act asa memory circuit which stores from cycle to cycle the positive peakvoltage from the sensing means 20. The DC signal from the capacitor 25acts upon the threshold detection means 29. When, as above mentioned,the motor 15 is of the typical 1/3 horsepower, I I5 volt type, thedevice 29 may be calibrated to break-over at voltages in excess of 10 to12 volts. Thus, when the main winding is initially energized by closingswitch 9, the peak voltage from the sensing transformer 20 into thememory circuit will be about I8 volts, as previously mentioned. Thus theDC voltage from the memory circuit will be about 18 volts, and thus thezener diode 29 will break over, thereby allowing a DC current to flowinto the gate of the bidirectional semiconductor switch 27, therebytriggering the switch into conduction, and thereby energizing thestarting winding 17. As normal speed is approached by the rotor of themotor 15, the current through the primary portion 20a of the transformer20 will fall, reducing the voltage appearing across the secondaryportion 20b of the transformer. When the peak value of this voltagereaches the break-over level of the zener diode 29, the DC current tothe gate of the bidirectional switch 27 will cease and the startingwinding 17 will be deenergized. For example, the normal running currentof a typical 1/3 horsepower, I15 volt motor is on the order of 6amperes. Thus, the peak voltage appearing across the secondary portion20b of the transformer 20 will be well below the exemplary breakovervoltage (of IO to I2 volts) of the zener diode 29. As a consequence, thezener diode 29 will block the triggering current to the gate of thebi-directional switch 27.

In the embodiment of FIG. 1 the transformer 20 comprises the sensingmeans; the diode 23 and capacitor 25 comprise the memory circuit; andthe break-over device 29 comprises the detcction means.

FIG. 2 illustrates the application of the principle of the presentinvention to a dishwashing machine wherein the typical type of timer isreplaced by an integrated logic circuit controlling allelectromechanical machine components with low power output signals. Suchan appliance is taught in the copending application Ser. No. 138,265,filed April 29, 1971, in the names of STEVEN B. SAMPLE, PAUL R.SCI-IEUER, STEVAN W. SPEI-IEGER AND KARMEN D. COX, and entitled CONTROLSYSTEM FOR APPLIANCES AND THE LIKE.

In FIG. 2, details of the machine circuit not pertinent to theparticular application taught have been omitted for purposes ofsimplicity. The integrated logic circuit is diagrammatically indicatedat 30. An induction motor is diagrammatically indicated at 31. In thisinstance, however, the motor 31 is shown as having a main or runningwinding 32 and two starting windings 33 and 34 for clockwise andcounter-clockwise rotation of the rotor, respectively. It is common inmodern dishwashers to use an induction motor for driving a pump. In onedirection of rotation, the pump recirculates washing fluids within thedishwasher vat. In the other direction of rotation, the pump dischargesfluids from the dishwasher vat through drain means.

The running winding 32 is connected to a source of AC electrical energy35 by a lead 36 and leads 37 and 38. It will be noted that lead 36contains a protective device such as a circuit breaker 39, similar tothe protective device 18 in FIG. 1. Lead 37 contains the primary portion40a of a sensing transformer 40, equivalent to the transformer 20 inFIG. 1.

The starting windings 33 and 34 are connected to the lead 36 (and thusto the source of electrical energy) by lead 41. The starting windings 33and 34 are also connected to the lead 38 (completing the circuit to thesource of electrical energy) by leads 42 and 43, respectively.

It will be noted that leads 37, 42 and 43 each contain a bi-directionalsemiconductor switch 44, 45 and 46, respectively. Thus, the operation ofthe main or running winding 32 is controlled by the bi-directionalswitch 44, while the starting windings 33 and 34 are controlled by thebi-directional switches 45 and 46, respectively.

The integrated logic circuit is diagrammatically shown as having anoutput for each of the motor windings. Thus, output 47 is shown asconnected to the gate of the bi-directional switch 44, controlling therunning winding 32. The output 47 produces a current limited DC signalwhen motor operation is desired. This signal triggers the gate ofbi-directional switch 44, thereby completing the connection of therunning winding 32 to the source of electrical power. As will bedescribed hereinafter, outputs 48 and 49 produce current-limited DCsignals intended to control starting windings 33 and 34, respectively.

As in the case of the embodiment of FIG. 1, the sensing transformer 40has a secondary portion 40b with leads 50 and 51. The lead 51 contains arectifying diode 52 of any suitable type and similar to the rectifyingdiode 23 of FIG. 1. The leads 50 and 51 are connected by lead 53containing a capacitor 54. The capacitor 54 serves much the samepurposes as the capacitor 25 in FIG. 1. The diode 52 and the capacitor54 comprise the memory circuit similar to the memory circuit of FIG. 1except that in FIG. 2 the memory circuit stores from cycle to cycle thenegative peak voltage from the sensing means 40. The juncture of leads50 and 53 is connected to lead 38. The juncture of leads 53 and 51 isconnected to lead 55 containing a break-over device 56, of any suitabletype and comprising the detecting means. Again, for purposes of anexemplary showing, the threshold detection means is represented as abreak-over device comprising a zener diode 56. It will be noted that thezener diode 56 is connected to the collectors of two switchingtransistors 57 and 58. The output 48 of the logic circuit is connecteddirectly to the base of switching transistor 57, while the emitter ofswitching transistor 57 is connected to the gate of the bi-directionalswitch 45.

In similar fashion, output 49 of the logic circuit is connected directlyto the base of switching transistor 58. The emitter of this switchingtransistor is connected to the gate of bi-directional switch 46.

Thus it will be seen that the output of the zener diode 56 will energizethe gate of bi-directional switch 45 or the gate of bi-directionalswitch 46, depending upon which of the switching transistors 57 and 58is receiving a signal from its respective logic circuit output.

Whenever motor operation is desired, the output 47 of the logic systemand one or the other of outputs 48 and 49 will produce a signal,depending upon the desired direction of rotation of the motor rotor. Theoperation of the sensing transformer, rectifying means 52-, capacitor 54and break-over means 56 is substantially identical to that describedwith respect to the corresponding elements in the embodiment of FIG. 1.Thus, depending upon the desired direction of rotation, either startingwinding 33 or starting winding 34 will be energized whenever the initialhigh current drawn by running coil 32 is sensed by transformer 40, andthe voltage across the secondary portion 40b of the transformer has apeak value above the break-over point of the zener diode 56. Selectionbetween starting coil 33 and starting coil 34 will be made by the logiccircuit through output 48 and its respective switching transistor 57 oroutput 49 and its respective switching transistor 58. In this way, theoutput of zener diode 56 will energize the gate of either bi-directionalswitch 45 or bidirectional switch 46, thereby connecting starting coil33 or starting coil 34 to the source of electrical energy 35.

As in the case of the embodiment of FIG. 1, when the rotor of the motor31 approaches the normal running speed, the peak voltage across thesecondary portion 40b of the sensing transformer 40 will fall below thebreak-over level of the zener diode 56, the gate of bidirectional switch45 or bi-directional switch 46 will be deenergized, and starting winding33 or starting winding 34 will be disconnected from the power source 35.

FIG. 3 illustrates the application of a third embodiment of the presentinvention to a dishwashing machine having an integrated logic circuitcontrolling all electromechanical machine components, with low powersignals. Again details of the machine not pertinent to the presentinvention have been omitted for clarity.

In FIG. 3 the integrated logic circuit is diagrammatically indicated at59. The motor 60 is shown as having two starting windings 61 and 62 andone running or I main winding 63. The running winding 63 is connected toa source of electrical energy by the lead 65 and the leads 66, 67 and68. Lead 66 contains the primary portion 69a of a transformer 69,equivalent to transformer 40 and 20 in FIGS. 2 and l, and comprising thesensing means. The starting windings 62 and 61 are connected to the samesource of electrical energy through lead 65 and leads 70-71 and 72-73,respectively. Each of the windings 61, 62, 63 has a bi-directionalsemiconductor switch connected in series with it. The operation of themain winding 63 is controlled by the bi-directional semiconductor switch74, while the starting windings 61 and 62 are controlled by thebi-directional semiconductor switches 75 and 76 respectively. The actionof the circuit which causes the bidirectional semiconductor switches 75and 76 to operate will now be described.

The integrated logic circuit 59 is shown as having three outputterminals 80, 81 and 82. The integrated logic circuit is specificallydesigned to produce the following sets of signals at the outputterminals 80, 81 and 82.

In a first instance, when it is desired not to have the motor 60actuated, the main output terminal 80 is electrically connected toground potential or zero volts. The condition of the forward and reverseoutput terminals 81 and 82 has no effect on the circuit under thesecircumstances.

In a second instance, when it is desired to run the motor 60 in theforward direction, a low power negative DC signal will be present atboth the main and forward output terminals 80 and 81; the reverse outputterminal 82 will be held at zero volts.

In a third instance, when it is desired to run the motor in the reversedirection, a low power negative DC signal will be present at both themain and reverse output The output terminal 80 is connected by lead 77to the gate of a bi-directional semiconductor switch 74 which connectsthe motor main winding 63 to a source of electrical energy 64 throughthe primary portion 69a of a sensing transformer 69. The low power DCsignal at the gate of switch 74 causes switch 74 to be in the conductingstate resulting in a relatively high current flow through the primaryportion 69a of the transformer 69. This current causes a relatively highAC voltage to be induced in the secondary portion 69b of the transformer69. This AC signal is half-wave rectified by the action of the diode 83and the capacitor 84, these two elements comprising the memory circuit.It will be noted that the voltage appearing across the capacitor 84 isproportional to the current flowing in the main winding 63. When thevoltage which appears across the capacitor 84 is in excess of thebreak-over voltage of the zener diode 85 (the threshold detection means)a DC current will flow through the resistor 86 into the base of. thetransistor 87. Under the conditions just described, which will existduring the time that the motor is coming up to normal running speed, thetransistor 87, which is connected through a current limiting resistor 88to a DC power source 89, will be in a conducting state. The presence ofa DC signal at the forward output terminal 81, which is connected bylead 78 to the base of the switching transistor 90, causes transistor 90to be in the conducting state. Under these conditions the current fromthe supply 89 is passed to the gate of the bi-directional semiconductorswitch 76. This current causes switch 76 to be in the conducting statewhich connects the forward starting winding 62 to the source ofelectrical energy 64 through leads 65, 70, 71 and 68.

When the motor 60 approaches the normal running speed, the current inthe main winding 63 decreases as described earlier. This decrease causesa corresponding decrease in the voltage stored on the capacitor 84. Thecircuit is designed so that this voltage at normal running speed is lessthan the break-over voltage of the zener diode 85. This causes thecurrent to the base of the transistor 87 to be blocked, resulting in thetransistor 87 being turned off. This action serves to disconnect theswitching transistor 90 from the DC power supply 89 causing the currentin the gate of switch 76 to fall to zero which, in turn, causes thebi-directional semiconductor switch 76 to be in the non-conductingstate, thereby disconnecting the starting winding from the source ofelectrical energy 64.

During the forward motor starting action just described thebi-directional semiconductor switch 75, which controls the reversestarting winding, remains off due to the non-conducting state in whichthe transistor 91 is kept in the absence of a signal from the outputterminal 82.

The integrated logic circuit output terminal conditions of the abovethird mentioned instance (wherein the motor 60 will be activated in thereverse direction) result in the interchanging of the action of theswitching transistors 90 and 91 and of the (ii-directional semiconductorswitches 76 and 75. The action of the remaining parts of the circuit isidentical to the action described above with respect to the secondinstance.

For the conditions of the first instance (wherein the motor 60 is off)no action takes place since the bidirectional semiconductor switch 74remains in the non-conducting state which causes the main motor winding63 to be disconnected from the source of electrical energy 64. Thus alsothere is no output from the secondary 69b of the sensing transformer 69,and hence neither start winding 61 not 62 is energized.

It will be understood by those skilled in the art that, as compared tothe embodiment of FIG. 2, the addition of transistor 87, power source 89and related components to the circuit of FIG. 3 serves to decrease theamount of current which the starting circuit is required to supply tothe switching transistors by adding the step of amplification.

FIG. 4 illustrates an embodiment of the circuit of the present inventionwhen applied to a dishwashing machine or the like having a reversingmotor and a conventional timer. The reversing motor is diagrammaticallyrepresented by the broken line rectangle 92 and is shown as beingprovided with a main or running winding 93, a forward phase winding 94and a reverse phase winding 95. The conventional timer (which may be ofany of the above mentioned types) is indicated by the broken linerectangle 96 and is shown as having three switches therein, 97, 98 and99. It will again be understood by the one skilled in the art thatdetails of the machine circuit not pertinent to the particularapplication taught have been omitted for purposes of clarity.

A source of power is diagrammatically indicated at 100 and has leads 101and 102 extending therefrom. A lead 103 extends across leads 101 and 102and contains in series the timer switch 97, the main winding 93 and theprimary portion 104a of a sensing transformer 104, the sensing means. Alead 105 extends from lead 102 to one side of lead 108 and contains inseries timer switch 98 and forward phase winding 94. Similarly, a lead107 extends from lead 102 to the above mentioned side of lead 108 andcontains in series timer switch 99 and reverse phase winding 95. Theother side of lead 108 is connected to lead 101 and contains abidirectional semiconductor switch 106.

The secondary portion 104b of the sensing transformer 104 has leads 109and 110 extending therefrom. The lead 109 is connected to the lead 101.The lead 110 contains a rectifying diode 111 of any suitable type. Therectifying diode 111 is connected to a breakover device 112 by lead 113.The break-over device 112 can again be of any suitable type (asdescribed above) and for purposes of an exemplary showing is illustratedas being a zener diode. A capacitor 114 is connected between leads 101and 113 by lead 115. The diode 1 l1 and capacitor 1 14 comprise thememory circuit, while the break-over device 112 comprises the thresholddetection means.

The break-over device 112 is connected to the gate of the bi-directionalsemiconductor switch 106 by lead 1 16.

The operation of the circuit of FIG. 4 may be described as follows.

When the motor 92 is desired to be off, the switch 97 of the timer(which controls the main winding) will be open. As a consequence, nocurrent will flow to the main winding. The positions of timer switches98 and 99, which control phase windings 94 and 95 respectively, will beof no consequence because no current will pass through the primaryportion 104a of the transformer 104. As a consequence, no voltage willbe induced in the secondary portion 104b of the sensing transformer 104and the gate of the bi-directional semiconductor switch 106 will not beactivated, hence rendering this switch in the non-conducting state.

If the motor is desired to run in its forward direction, timer switches97 and 98 will be closed, while timer switch 99 will be open. When timerswitch 97 is closed, the main motor winding 93 and the primary portion104b of the sensing transformer 104 will receive current from the source100. As a consequence voltage will be induced in the secondary portionl04b of the sensing transformer. This last mentioned voltage will bepeak detected by the half-wave peak detector combination 114-111. The DCsignal from the peak detector combination will pass through break-overdevice 112 (so long as it is of sufficient magnitude to do so) andactivate the gates of the bi-directional semiconductor switch 106.

Under these conditions, bi-directional semiconductor switch 106 will berendered conducting and, since timer switch 98 is closed, the forwardphase winding 94 will be energized. However, since switch 99 is open,the reverse phase winding 95 will not be energized.

When it is desired for the motor 92 to run in reverse, the condition ofthe circuit will be the same as that de scribed with the motor runningforward, with the exception that timer switch 98 will be open and timerswitch 99 will be closed. Under these circumstances, the fact that thebi-directional semiconductor switch 106 is rendered conducting will, incombination with the fact that switch 99 is closed, cause the reversewinding 95 to be energized. However, since timer switch 98 is open, theforward phase winding 94 will not be energized.

In the embodiments thus far described, it is possible to substitute aresistance for the sensing transformer to serve as a sensing means forthe main winding current. The resistor has the advantage of being lesscostly and less space consuming. For purposes of an exemplary showing,FIG. illustrates a circuit substantially identical to that shown in FIG.3, but wherein a resistor is used as the sensing means. In FIG. 5, anintegrated logic circuit 117 having outputs 118, 119 and 120 is shown,and is equivalent to the integrated logic circuit 59 of FIG. 3 with itsoutputs 80, 81 and 82. A motor 121 is shown having a main winding 122and starting windings 123 and 124, equivalent to the motor 60 of FIG. 3with its main winding 63 and starting windings 62 and 61.

A source of electrical energy is diagrammatically indicated at 125 andhas leads 126 and 127 extending therefrom. The main winding 122 isconnected across leads 126 and 127 by lead 128. In similar fashion,starting windings 123 and 124 are connected across leads 126 and 127 byleads 129 and 130, respectively. The

lead 128 has, in series with the main winding 122, a bidirectionalsemiconductor switch 131, the gate of which is connected by lead 132 tothe output 118. The switch 131 is equivalent to the switch 74 of FIG. 3.Lead 129 has, in series with starting winding 123, a bidirectionalsemiconductor switch 133, equivalent to switch 76 of FIG. 3. Lead 130has, in series with starting winding 124, a bi-directional semiconductorswitch 134, equivalent to switch 75 of FIG. 3. The gate of thebi-directional semiconductor switch 133 is connected by lead 135 tooutput 119 through a switching transistor 136. The switching transistor136 is equivalent to transistor 90 of FIG. 3. In similar fashion, thegate of the bi-directional semiconductor switch 134 is connected throughlead 137 to output through switching transistor 138, equivalent totransistor 91 of FIG. 3.

It will be noted that the collectors of switching transistors 136 and138 are connected to the emitter of transistor 139. Transistor 139 isequivalent to transistor 87 of FIG. 3 and has its collector connectedthrough a current limiting resistor 140 to a DC power source 141, in thesame manner as taught with respect to FIG. 3.

The primary difference between the cricuit of FIG. 5 and the circuit ofFIG. 3 lies in the fact that the circuit of FIG. 5 does not include asensing transformer. Rather, the circuit includes a sensing resistor 142in the lead 128 and in series with the bi-directional semiconductorswitch 131 and the main winding 122. A lead 143 extends between the lead128 and the base of the transistor 139 and contains a diode 144, a zenerdiode 146a, and a resistor which are equivalent respectively to zenerdiode 83 and resistor 86 in FIG. 3. A capacitor 146 is connected acrossleads 127 and 143, and is equivalent to capacitor 84 in FIG. 3.

The operation of the circuit may be described as follows. When it isdesired to start the motor in the forward direction, a low-power DCsignal will be present at both the main and forward output terminals 118and 119 of the integrated logic circuit. The reverse output terminal 120will be held at zero volts.

The low-power DC signal from the output 118 will exist at the gate ofthe bi-directional semiconductor switch 131, rendering it in theconducting state. This results in a relatively high current flow throughthe resistor 142. The AC voltage appearing across the resistor 142 isproportional to the current through the resistor. This signal is peakdetected by the action of diode 144 and capacitor 146. It will beunderstood by one skilled in the art that the voltage appearing acrossthe capacitor 146 is proportional to the current flowing in the mainwinding 122.

When the voltage which appears across the capacitor 146 is in excess ofthe break-over voltage of the zener diode 146a, current flows throughthe resistor 145 to the base of transistor 139, thereby causingtransistor 139 to conduct. Since the transistor 139 is connected to a DCpower source 141 through the current limiting resistor 140, a DC signalwill be present at the collectors of switching transistor 136 and 138.Since a lowpower DC signal is present at the base of switchingtransistor 136 from the output 119 of the integrated logic circuit, theswitching transistor will be in the conducting state and will, in turn,energize the gate of the bi-directional semiconductor switch 133rendering it conductive. Under these conditions, the forward startingwinding 123 will be connected to the source of electrical energy 125.

At the same time, although a signal exists at the collector of switchingtransistor 138, since no signal exists at its base from the output 120,it will not be rendered conductive. As a consequence, the gate of thebidirectional semiconductor switch 134 will not be energized and thatswitch will be non-conductive. Thus, the reverse starting winding willnot be energized.

When the motor 121 approaches the normal running speed and the currentin the main winding 122 decreases, this decrease causes a correspondingdecrease in the voltage stored in capacitor 146. The circuit is sodesigned that this voltage will be less than the breakover voltage ofzener diode 146a, and thus current will not flow through resistor 145 tothe base of transistor 139, and thus transistor 139 will be renderednonconductive. This action serves to block the flow of current throughswitching transistor 136, and hence the current into the gate of thebi-directional semiconductor switch 133 falls to zero. This, in turn,causes the bidirectional semiconductor switch 133 to be in thenonconducting state, thereby disconnecting the forward starting windingfrom the source of electrical energy 125.

The integrated logic circuit output terminal conditions when the motoris to be activated in the reverse direction are such as to result in theinterchanging of the action of switching transistors 136 and 138 and ofthe bi-directional semiconductor switches 133 and 134. The action of theremaining part of the circuit is identical to that described above, andthe reverse starting winding will be energized until the motorapproaches its normal running speed, whereupon the reverse motor windingwill be de-energized. The forward starting winding will remainde-energized under these conditions.

Under those circumstances when the motor 121 is in its of condition, noaction takes place since no signal is sent to the gate of thebi-directional semiconductor switch 131 from output 118 of theintegrated logic circuit. Therefore, the switch 131 remains in thenonconducting state and the main motor winding 122 remains disconnectedfrom the source of electrical energy 125. Thus also there is no voltagedeveloped at the sensing resistor and hence transistor 139 isnonconductive, and hence neither starting winding 123 not 124 isenergized.

In similar fashion, a sensing resistor may be substituted for thesensing transformer 40 in FIG. 2. This is illustrated in FIG. 7, whereinlike parts have been given like index numerals. The sensing resistor isshown at 400 in lead 37 in series with the main or running winding 32.With the exception of the use of a sensing resistor, rather than atransformer, the operation of the circuit of FIG. 7 is substantiallyidentical to that described with respect to FIG. 2.

In those embodiments described above in which the voltage to be detectedby the threshold detecting means is sufficiently high, it is possible tosubstitute a glow lamp or other bi-directional break-over device for theundirectional zener diode.

FIG. 6 illustrates a simple circuit wherein a glow lamp is used. Asource of electrical energy is indicated at 147 with leads 148 and 149extending thereffrom. A motor is shown by the broken line rectangle 150and is provided with a main winding 151 and a starting winding 152. Themain winding is connected across leads 148 and 149 by lead 153. The lead153 contains, in series with the main winding 151, the primary portion154a of a transformer 154. For purposes of this exemplary showing, thelead 153 is also illustrated as having a bi-directional semiconductorswitch 155 with its gate connected by lead 156 to an output signalsource 157. It will be understood, however, that the switch 155 might bea switch constituting a part of a conventional mechanical timing device.The secondary portion of the transformer 154 is connected by lead 158 tothe lead 149. The secondary portion l54b is connected to a memorycircuit comprising a peak detecting diode 158a and capacitor 158b. Thememory circuit is connected to a threshold detection means comprising aglow lamp 162. The glow lamp is connected through resistor 163 to thegate of a bi-directional semiconductor switch 160 which is in seriesconnection with the starting winding 152 via lead 161. Lead 161 isconnected across leads 148 and 149.

When the motor is to be energized, a signal is transmitted to the gateof the bi-directional semiconductor switch from output 157. Switch 155is then rendered in the conducting state and the main winding 151 isconnected across leads 148 and 149 and is therefore connected to thesource of electrical energy 147. Under these circumstances, thebi-directional semiconductor switch is triggered into conduction sincethe output of the current sensing transformer 154 and thus the memorycircuit will be in excess of the break-over voltage of the glow lamp162. When the motor 150 approaches normal running speed, the output ofthe current sensing transformer and thus the memory circuit will fallbelow the break-over voltage of the glow lamp 162, the bi-directionalsemiconductor switch 160 will be rendered non-conductive and thestarting winding 152 will be disconnected from the source of electricalenergy.

FIG. 8 is a block diagram illustrating the primary elements of thestarting circuits of the present invention. As indicated in the diagramof FIG. 8, the motor main winding current is sensed by a sensing means164 which may take the form of a transformer or a sensing resistor. Thesensing means procides an instantaneous output proportional to thecurrent through the main motor winding. The output of the sensing meansmay be fed to a memory circuit 165 which will convert the sensing meansoutput to a slowing varying DC voltage proportional to the peak currentin the main motor winding. The memory circuit may take a number offorms, as for example the peak detecting diode-capacitor combinations(which may include a resistor if the circuit requires it) as describedabove, or a digital memory circuit, as will be illustrated hereinafter.The output of the memory circuit may then be fed into a thresholddetection means 166 which determines when the starting winding will beturned on and turned off. The output of the threshold detection means165 may go directly to the gate of an interfacing device (as in the caseof the embodiments of FIGS. 1 and 4), or it may go to the bases ofswitching transistors as shown, for example, in FIGS. 2, 3, 5 and 7.Alternatively, the output of the threshold detecting means may go to alogic circuit which, in turn, will determine which of the startingwindings (if there is more than one) will be actuated.

FIG. 9 is similar to FIG. 8 and like parts have been given like indexnumerals. The purpose of FIG. 9 is simply to illustrate that the outputof the sensing means may be fed to the threshold detection means, andthe output of the threshold detection means may then be fed to a memorycircuit, as will be shown hereinafter.

In the starting circuits thus far described, the threshold detectionmeans has been a single-level one (i.e., the threshold point for turningon the starting winding has been the same as the threshold for turningoff the starting winding). In many applications of these circuits, sucha single-level threshold detection means is adequate. However,difficulty may arise when the difference between the sensed voltageduring the starting condition of the motor and the sensed voltage duringthe running condition is relatively small, since under thesecircumstances the transistion through the turn off point occurs throughmany cycles. Under such conditions, a single threshold point may not beadequate. Therefore, it is frequently desirable to have a firstthreshold for turning on the starting winding and a second threshold forturning off the starting winding, with the turn on threshold beinghigher than the turn off threshold. The he use of a'bi-level thresholddetection means assures that once the starting winding is turned off, itwill not be turned on again until the motor is turned off and restarted.The use of a bi-level threshold means also aids in designing variance inthe line current, temperature problems and the like. It also lendsitself well to mass production of the appliance, relieving the necessityof selecting the components for the motor starting circuit with greataccuracy and individually for each appliance. The above noted problemsare even more acute when a sensing resistor is used as a sensing means,since in general the voltages from a sensing resistor are quite small.

FIG. 10 is a simplified, incomplete circuit diagram illustrating theprimary components set forth in FIG. 8, and like parts have been givenlike index numerals. Thus, a sensing resistor is illustrated at 164, thememory circuit is is shown by the dashed rectangle at 165 and thethreshold detection means is shown by the dashed rectangle at 166. Themotor main winding is shown at 167.

The memory circuit 165 comprises a rectifying diode 168, a capacitor 169and a resistor 170. This memory circuit is similar to those describedabove.

The threshold detection means 166 is a bi-level detection means. Thebi-level detection means comprises a Schmitt trigger. The Schmitttrigger, in and of itself, is well known to the skilled worker in theart and comprises a pair of transistors 171 and 172, collector resistors173 and 174, a resistor 175 connected to the base of the transistor 172and the common emitter resistor 176 connected to ground. The output ofthe Schmitt trigger is shown at 177 and an input from a DC power sourceis shown at 178. As is well known to the worker skilled in the art, theSchmitt trigger will provide a turn on threshold and a turn offthreshold, which can be adjusted independantly by adjusting the valuesof the collector resistors 173 and 174 and a common emitter resistor176. The Schmitt trigger is also characterized by a snap-action,particularly desirable for the circuits of the present invention. In thediagram of FIG. 10, the output 177 of the Schmitt trigger will be apositive voltage approximately equivalent to the DC voltage input at 178when the starting winding is to be turned on. Otherwise, the output at177 will be approximately zero.

FIG. 11 is similar to FIG. 10, and like parts have been given like indexnumerals. In this instance, however, the rectifying diode 168a has beenreversed, and the DC input at 178 is a negative DC voltage. Under thesecircumstances, the output at 177, when the starting winding is to beturned on, will be a negative voltage approximately equal to thenegative DC voltage at input 178. Otherwise, the output at 177 will beapproximately zero.

FIG. 12 is again similar to FIGS. 10 and 11 (like parts having beengiven like index numerals), but it illustrates the primary components inthe order shown in FIG. 9. Thus, the output 177 of the Schmitt triggerdrives the memory circuit 165. The output of the memory circuit isindicated at 179. When the starting wind ing is to be turned on, theoutput 179 will have a negative voltage approximately equal to thenegative DC voltage at the input 178 of the Schmitt trigger. Otherwise,the output 179 will be approximately zero.

It should be noted that the circuit of FIG. 12 behaves as though thelevel detection means were single level rather than bi-level. Thisbehavior occurs because the sinusoidal voltage from the sensing resistor164 is being led directly to the input of the Schmitt trigger throughresistor a. Thus. assuming the current in the main winding 167 is equalto or in excess of the level for which the starting winding is required,a strong negative voltage (approximately equal to the DC voltage 178)appears at 177, whenever the negative-going voltage across the sensingresistor 164 during the negative half period of the sinusoidal currentthrough the main winding 167 exceeds in magnitude the turn-on level ofthe Schmitt trigger. The voltage at output 177 then reverts toessentially zero whenever the positive-going voltage across the sensingresistor 164 during the aforementioned negative half period is smallerin magnitude than the turn off level of the Schmitt trigger, and remainsessentially zero during the positive half period of the sinusoidalcurrent through the main winding 167. The memory circuit 168a through170 then peakdetects the periodic transistions of the output 177 of theSchmitt trigger, and hence the output 179 exhibits a steady voltageessentially equal to the DC voltage at 178. When the current in the mainwinding 167 is below the level for which a start winding is required,the negative voltage from the sensing resistor never exceeds inmagnitude the turn-on level of the Schmitt trigger, and thus bothoutputs 177 and 179 are steady at essentially zero volts.

FIG. 13 is similar to FIG. 12 and like parts have been given like indexnumerals. In this instance, however, the memory circuit 165a isillustrated as being a digital memory curcuit. The memory circuit 165ais illustrated in the form of a logic diagram comprising a clock orpulse source 180 driving a digital counter 181 having a plurality ofstages. The clock may comprise any suitable well known circuit and maybe of the type which derives pulses from the line current. The digitalcounter is illustrated as having three stages 182, 183 and 184. Thethree dots between stages 183 and 184 are intended to indicate thatadditional stages may be present. The Q output 185 of the final stage184 (i.e., the output of the digital counter 181) is connected to thereset input of a flip-flop 186. The Q output 187 of the flip-flop 186 isthe output of the memory circuit.

The output 177 of the Schmitt trigger is connected to the reset input ofeach of the stages 182-184 of the digital counter 181. The output 177 issimilarly connected to the set input of flip-flop 186. Thus, when thestarting winding is to be turned on, the output 177 of the Schmitttrigger will send a logical one signal during part of each negative halfperiod, as described above, to the reset input of each of the stages ofthe digital counter 181 so that the output 185 of the counter will belogical zero. Thus, a logical zero will appear at the reset input offlip-flop 186, while a logical one from the output 177 of the Schmitttrigger will appear at the set input of the flip-flop. As a result, theoutput of the memory circuit 165a at 187 will be logical. The period ofthe counter is greater than the period of the sinusoidal line power tothe motor, and thus the output 187 of the memory circuit will remainlogical one, even though the output 177 of the Schmitt trigger isfluctuating between logical one and logical zero at the frequency of thesinusoidal line power to the motor, as described previously.

When the starting winding is to be turned off, the output of the Schmitttrigger at 177 will be continuously logical zero. This logical zero willappear at the reset inputs of the digital counter stages 182-184, and atthe set input of flip-flop 186. The output of the digital counter at 185will remain logical one until the counter completes its full countwhereupon the Q output of stage 184 will make a logical zero-logical onetransition, providing a logical one at the reset input of flipflop 186.When this happens, the output 187 of the memory circuit 165 will shiftfrom logical one to logical zero.

All of the embodiments illustrated in FIGS. through 13 have beenillustrated as using a sensing resistor as a sensing means. It will beunderstood by one skilled in the art that a sensing transformer could beused after the manner described with respect to FIGS. 1 through 4.

When the memory circuit precedes the Schmitt trigger (as in FIGS. 8, 10and 11) the memory circuit 165 provides a slowly varying signal which isconverted to a definite output signal by the Schmitt trigger 166, as theon and off thresholds are reached. As the input to the Schmitt triggerreaches the start threshold level, the Schmitt trigger becomes unstablein the off state and mades a transition to the on state. where it isstable. This transition is characterized by a snap-action. As the inputto the Schmitt trigger reaches the stop threshold, the Schmitt triggerbecomes unstable in the on state and makes a transition to the off statewith the same snap-action characteristic. Thus a slowly varying orbarely adequate signal from the memory circuit 165 is converted to adefinite signal by the Schmitt trigger with a snap-action.

When the memory circuit follows the Schmitt trigger (as in FIGS. 9, l2and 13) the input of the Schmitt trigger is connected directly to theinstantaneous output of the sensing means. As previously described, asthe motor starts up the Schmitt trigger will snap on and off at thepower line frequency each time the peak of the sensed current exceedsthe turn on threshold until the motor reaches its normal operating speedand the peak of the sensed current no longer exceeds the turn onthreshold, whereupon the Schmitt trigger will become stable in the offcondition. The memory circuit will serve to maintain an on signal untilthe output of the Schmitt trigger becomes stable in the off condition.

FIG. 14 illustrates the embodiment of FIG. 2 provided with a bi-levelthreshold detection means. Like parts have been given the same indexnumerals appearing in FIG. 2. In essence, the zener diode 56 of FIG. 2has been replaced by the Schmitt trigger 188 and the resistor 189. Forpurposes of clarity, the components of the Schmitt trigger have beengiven the same index numerals as applied in FIGS. 10 through 13.

The input of the Schmitt trigger 188 is connected to lead 55. The output177 of the Schmitt trigger is connected to the collectors of the twoswitching transistors 57 and 58. The resistor 176 is grounded to lead38.

The operation of the embodiment of FIG. 14 will be substantiallyidentical to the operation described with respect to FIG. 2. Thepresence of the bi-level threshold detecting means or Schmitt trigger188, however, will assure that there will be a first threshold forturning on either of the starting windings 33 and 34, and a secondthreshold for turning off either of these starting windups. The firstthreshold will be at a higher voltage level than the second. It will beunderstood by one skilled in the art that the bi-level thresholddetection means 188 could be applied to the embodiment of FIG. 7. Itwill be remembered that FIG. 7 differs from FIG. 2 only in that thesensing resistor 40c is substituted for the sensing transformer 40.

It will be readily understood that FIG. 14 conforms to the block diagramof FIG. 8. The transformer 40 is equivalent to the sensing means 164 ofFIG. 8. The diode 52, capacitor 54 and resistor 189 constitute thememory circuit equivalent to memory circuit of FIG. 8. Finally, theSchmitt trigger 188 corresponds to the threshold detecting means 165 ofFIG. 8.

FIG. 15 illustrates the application ofa bi-level threshold detectingmeans to the embodiment of FIG. 3. For purposes of clarity, like partshave been given index numerals corresponding to those in FIG. 3. Thebi-Ievel threshold detecting means (a Schmitt trigger) is generallyindicated at 190. It will be noted that FIG. 15 differs from FIG. 3 inthat the secondary winding 69b, of the transformer 69, the capacitor 84and the resistor 176 are grounded to lead 68.

It will be evident that the embodiment of FIG. 15 is substantiallyidentical to that of FIG. 14, differing only in that the output 177 ofthe Schmitt trigger is connected to an amplification circuit comprisingelements 86 through 89. With this exception, the operation of FIG. 15 isidentical to that described with respect to FIG. 14. It will beunderstood that the DC power source at 89 for the amplification circuitcan be the same DC power source as is connected to the input 178 of theSchmitt trigger 190.

FIG. 15 again conforms to the block diagram of FIG. 8. The sensing meanscomprises the transformer 69. the memory circuit comprises the diode 83,capacitor 84 and resistor 191. The bi-level threshold detection meanscomprises the Schmitt trigger 190.

FIG. 16 illustrates the provision of a bi-level threshold detectionmeans to the circuit illustrated in FIG. 5. For purposes of clarity,like parts have been given the same index numerals as appear in FIG. 5.The bi-level threshold detection means is generally indicated at 192,and the components thereof have been given the same index numerals asappear in FIGS. 10 through 13.

That portion of the circuit of FIG. 16 shown in solid lines issubstantially equivalent to that of FIG. 14 with the exception that asensing resistor 142 is used, rather than the sensing transformer 40 ofFIG. 14. The operation of the circuit of FIG. 16 is otherwise the same.The output of the Schmitt trigger 192 is connected directly to thecollectors of switching transistors 136 and 138.

FIG. 16 also illustrates, in dotted lines, an amplification circuitidentical to that shown in FIG. 5 and comprising elements 139, 140, 141and 145. When the amplification circuit is to be used, there will be noconnection between the points A and B. FIG. 15 is again an example of anarrangement of the primary elements in the order shown in FIG. 8. Thesensing means comprises the sensing resistor 142. The memory circuitcomprises the diode 144, capacitor 146 and resistor 193. The bilevelthreshold detecting means comprises the Schmitt trigger 192.

FIG. 17 illustrates the embodiment of FIG. 16 with the output of theSchmitt trigger going to the logic circuit. Like parts have been givenlike index numerals. The embodiment of FIG. 17 is substantiallyidentical to that of FIG. 16 except that the output 177 of Schmitttrigger 192 goes to an input 194 of the logic circuit 117. It will benoted that the switching transistors 136 and 138 of FIG. 16 have beeneliminated, since the logic circuit will perform their function. As aconsequence, the gate of the interfacing device 133 can be connecteddirectly to the output 119 of the logic circuit, via lead 135.Similarly, the interfacing device 134 may be connected to the logiccircuit output 120 via lead 137.

When the motor is started, the current through the main winding 122 willbe sensed by the sensing resistor 142 and the memory circuit comprisingdiode 144, capacitor 146 and resistor 193. When the start threshold(established by the Schmitt trigger 192) is reached, the Schmitt triggerwill provide a logical one at its output 177. This logical one willcause the logic circuit 117 to have a logical one at either its output119 or its output 120. The logic circuit will also select which of theseoutputs will have the logical one signal. In this way, the selected oneof interfacing devices 133 and 134 will be rendered conductive and theselected one of starting windings 123 and 124 will be energized.

When the motor reaches its normal running speed, the sensed current inmain winding 122 will diminish to the point where the Schmitt trigger192 will become unstable in its on condition and will snap to its offcondition providing a logical zero at its output 177. This logical zerowill appear at both outputs 119 and 120 of the logic circuit 117 withthe result that the previously selected one of interfacing devices 133and 134 will become nonconductive and the selected one of startingwindings 123 and 124 will be turned off. The starting winding which wasnot selected will, of course, remain deenergized.

FIG. 18 is similar to FIG. 17 and like parts have been given like indexnumerals. FIG. 18 differs from FIG. 17 in that the memory circuit (i.e.,the diode 144, the capacitor 146 and the resistor 193) have beeneliminated. In this embodiment, the function of the memory circuit hasbeen incorporated in the logic circuit 117, in a manner similar to thatshown in FIG. 13. The resistor 195 simply serves as a protectiveresistor for the Schmitt trigger 192.

The operation of FIG. 18 will be substantially identical to thatdescribed with respect to FIG. 17, with the exception that the functionof the memory circuit is performed by the logic circuit 117, in a mannersimilar to that shown in FIG. 13. Since this is true, the embodiment ofFIG. 18 has the primary elements in the arrangement shown in FIG. 9,above.

FIG. 19 is similar to FIG. 18 and like parts have been given like indexnumerals. FIG. 19 differs from FIG. 18 in that the logic circuit 117incorporates most of the bilevel threshold detection means, or Schmitttrigger. Thus, the transistor 171 will be connected to a pair of inputs196 and 197 in the logic circuit. Again, the resistor 198 serves thesame purpose as resistor 195 of FIG. 18, acting as a protective resistorfor transistor 171. Thus, in the circuit shown in solid lines in FIG.19, the logic circuit 117 performs the functions of both the memorycircuit and the major portion of the Schmitt trigger.

The diode 144 and capacitor 146 are shown in dotted lines in FIG. 19.This is to indicate that a memory circuit of the type shown in FIG. 17may be incorporated ahead of the transistor 171. Under thesecircumstances, the resistor 198 serves as a part of the memory circuitand the logic circuit 117 no longer performs the function of the memorycircuit.

The operation of the circuit of FIG. 19 (as shown in solid lines) issubstantially the same as that of the circuit of FIG. 18, with theexception that the logic circuit 117 will perform a part of the functionof the bi-level threshold detection means. Thus, this circuit conformsto the diagram of FIG. 9. Ifa memory circuit is incorporated (as shownin dotted lines) this circuit then conforms to the diagram of FIG. 8 andperforms in substantially the same manner as that described with respectto FIG. 17, again with the exception that the logic circuit 117 willperform a part of the function of the bilevel threshold detection means.

FIG. 20 is similar to FIG. 19 and like parts have been given like indexnumerals. FIG. 20 is simply intended to show that the logic circuit 117may incorporate both the function of the threshold detection means andthe function of the memory circuit. Under these circumstances, an input199 of the logic circuit will be connected directly to the sensingresistor 142 by lead 200. The operation of FIG. 20 will otherwise besubstantially identical to that described with respect to FIGS. 17through 19.

It will be understood by one skilled in the art that in any of thecircuits illustrated in FIGS. 17 through 20, a sensing transformer maybe substituted for the sensing resistor 142. This is illustrated, forexample, in FIG. 20 wherein a sensing transformer is shown in dottedlines at 201. It will be understood that when transformer 201 is used,the resistor 142 will be eliminated, as will the connections between theterminals of the transformer primary and secondary.

Modifications may be made in the invention without departing from thespirit of it.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

l. A circuit for the automatic starting of an induction motor of thetype having a main running winding, a first starting winding and asecond starting winding to cause said motor to run in a directionopposite to that initiated by said first starting winding, said circuitcomprising a source of electrical energy and first and second leadstherefrom, a third lead containing in series said main running windingand means for sensing the current drawn by said main running winding andproducing an electric signal proportional thereto, a fourth leadcontaining in series said first starting winding and a firstbi-directional semi-conductor switch, a fifth lead, said fifth leadcontaining in series said second starting winding and a secondbi-directional semi-conductor switch, means to connect and disconnectsaid third, fourth and fifth leads across said first and second leads,means for conducting said sensing means signal to start and stopthreshold detecting means calibrated to pass a start signal at voltagesin excess of that voltage sensing means signal which exists when saidmotor is running at nor-' mal speed, an integrated logic circuit havingfirst, second and third outputs, said means for connecting anddisconnecting said third lead across said first and second leadscomprising a third bi-directional semiconductor switch connected inseries with said main running winding and said sensing means in saidthird lead, said first output of said integrated logic circuit

1. A circuit for the automatic starting of an induction motor of thetype having a main running winding, a first starting winding and asecond starting winding to cause said motor to run in a directionopposite to that initiated by said first starting winding, said circuitcomprising a source of electrical energy and first and second leadstherefrom, a third lead containing in series said main running windingand means for sensing the current drawn by said main running winding andproducing an electric signal proportional thereto, a fourth leadcontaining in series said first starting winding and a firstbi-directional semi-conductor switch, a fifth lead, said fifth leadcontaining in series said second starting winding and a secondbidirectional semi-conductor switch, means to connect and disconnectsaid third, fourth and fifth leads across said first and second leads,means for conducting said sensing means signal to a start and stopthreshold detecting means calibrated to pass a start signal at voltagesin excess of that voltage sensing means signal which exists when saidmotor is running at normal speed, an integrated logic circuit havingfirst, second and third outputs, said means for connecting anddisconnecting said third lead across said first and second leadscomprising a third bidirectional semi-conductor switch connected inseries with said main running winding and said sensing means in saidthird lead, said first output of said integrated logic circuit beingconnected to the gate of said third bi-directional semi-conductorswitch, said means for connecting aNd disconnecting said fourth andfifth leads across said first and second leads comprising a firstswitching transistor and a second switching transistor, said thresholddetecting means being connected to the collectors of said first andsecond switching transistors, the emitters of said first and secondtransistors being connected to the gates of said first and secondbi-directional semi-conductor switches respectively, said second andthird outputs of said integrated logic circuit being connected to thebases of said first and second switching transistors respectively,whereby when said first and second logic circuit outputs provide alogical 1 at the gate of said third bi-directional semi-conductor switchand the base of said first switching transistor respectively, and saidthird output provides a logical zero at the base of said secondswitching transistor, said third and fourth leads are connected acrosssaid first and second leads and said fifth lead is disconnectedtherefrom, said main winding will be energized, said second startingwinding will be deenergized and said first starting winding will beenergized for so long as said threshold detecting means transmits saidstart signal, and when said first and third logic circuit outputsprovide a logical 1 at the gate of said third bi-directionalsemi-conductor switch and the base of said second switching transistorrespectively, and said second output provides a logical zero at the baseof said first switching transistor, said third and fifth leads areconnected across said first and second leads and said fourth lead isdisconnected therefrom, said main running winding will be energized,said first starting winding will be deenergized and said second startingwinding will be energized for so long as said threshold detecting meanstransmits said start signal.
 2. The structure claimed in claim 1 whereinsaid current sensing means comprises a transformer, said trnasformerhaving a primary portion in series with said main motor winding in saidthird lead, said transformer having a secondary portion, saidproportional signal being induced in said secondary portion.
 3. Thestructure claimed in claim 1 wherein said means for sensing the currentdrawn by said main running winding comprises a resistor in series withsaid main running winding in said third lead.
 4. The structure claimedin claim 1 wherein said means for conducting said sensing means signalto said threshold detecting device is a memory circuit comprising adiode-capacitor half-wave rectifier in series with a resistor being soconnected between said second and third leads that the DC voltageappearing across said capacitor is proportional to the current flowingin said main running winding.
 5. The structure claimed in claim 1wherein said threshold detecting means is a single level detectingmeans.
 6. The structure claimed in claim 1 wherein said thresholddetecting means is a bi-level detecting means calibrated to initiatesaid start signal at a first sensed voltage level and to terminate saidstart signal at a second sensed voltage level, said first sensed voltagelevel being higher than said second sensed voltage lead.
 7. Thestructure claimed in claim 1 including a third switching transistorbetween said threshold detecting means and said first and secondswitching transistors, said threshold detecting means being connectedthrough a first resistor to the base of said third switching transistor,the collector of said third switching transistor being connected througha second resistor to a source of DC power, the emittor of said thirdswitching transistor being connected to the collectors of said first andsecond switching transistors.
 8. The structure claimed in claim 4wherein said memory circuit has an output connected to said thresholddetecting means, said threshold detecting means being a single leveldetecting means.
 9. The structure claimed in claim 4 wherein said memorycircuit has an output connected to said tHreshold detecting means, saidthreshold detecting means being a bi-level detecting means calibrated toinitiate said start signal at a first sensed voltage level and toterminate said start signal at a second sensed voltage level, said firstsensed voltage level being higher than said second sensed voltage level.10. The structure claimed in claim 5 wherein said threshold detectingmeans comprises a zener diode.
 11. The structure claimed in claim 5wherein said threshold detecting means comprises a resistor.
 12. Thestructure claimed in claim 6 wherein said bi-level detecting meanscomprises a Schmitt trigger and a source of DC current for said Schmitttrigger.
 13. The structure claimed in claim 6 wherein said thresholddetecting means has an input to receive the output of said sensingmeans, a memory circuit in said connection between said detecting meansand said collectors of said first and second switching transistors, saidmemory circuit comprising a diode-capacitor half-wave rectifier inseries with a resistor.
 14. The structure claimed in claim 9 whereinsaid bi-level detecting means comprises a Schmitt trigger and a sourceof DC current for said Schmitt trigger.
 15. The structure claimed inclaim 9 including a third switching transistor between said thresholddetecting means and said first and second switching transistors, saidthreshold detecting means being connected through a first resistor tothe base of said third switching transistor, the collector of said thirdswitching transistor being connected through a second resistor to asource of DC power, the emittor of said third switching transistor beingconnected to the collectors of said first and second switchingtransistors.
 16. The structure claimed in claim 9 wherein said logiccircuit incorporates said first and second switching transistors, saidsecond and third outputs of said logic circuit being connected directlyto said gates of said first and second bi-directional semi-conductorswitches, said logic circuit having an input for said start signal fromsaid threshold detecting means.
 17. The structure claimed in claim 9wherein said logic circuit incorporates said first and second switchingtransistors, said second and third outputs of said logic circuit beingconnected directly to said gates of said first and second bi-directionalsemi-conductor switches, said logic circuit incorporating a part atleast of said threshold detecting means.
 18. The structure claimed inclaim 9 wherein said logic circuit incorporates said first and secondswitching transistors, said second and third outputs of said logiccircuit being connected directly to said gates of said first and secondbi-directional semi-conductor switches, said logic circuit incorporatingsaid memory circuit and said threshold detecting means and having aninput for a signal from said sensing means.
 19. The structure claimed inclaim 13 wherein said logic circuit incorporates said first and secondswitching transistors, said second and third outputs of said logiccircuit being connected directly to said gates of said first and secondbi-directional semi-conductor switches, said logic circuit incorporatingsaid memory circuit and having an input for said start signal from saidthreshold detecting means.
 20. The structure claimed in claim 13 whereinsaid logic circuit incorporates said first and second switchingtransistors, said second and third outputs of said logic circuit beingconnected directly to said gates of said first and second bi-directionalsemi-conductor switches, said logic circuit incorporating said memorycircuit and said threshold detecting means and having an input for asignal from said sensing means.